Active matrix and intrinsic photoconductive polymer of a linear polysiloxane

ABSTRACT

and   in the presence of tetramethylammonium silanolate or corresponding alkali metal salt as initiators; the polymeric product, and photoconductive members utilizing such product demonstrate excellent structural and electronic properties for xerographic purposes.   A process for obtaining a substantially linear homopolymer and/or copolymeric material from a cyclic trimer such as 1,3,5trimethyl-1,3,5-tri(N-ethyl-3-carbazyl)cyclotrisiloxane alone or in combination with cyclic trimers or tetramers exemplified by the formulae

United States Patent [1 1 Limburg [451 Aug. 12, 1975 ACTIVE MATRIX ANDINTRINSIC PI-IOTOCONDUCTIVE POLYMER OF A LINEAR POLYSILOXANE [75]Inventor: William W. Limburg, Penfield, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: May 7, 1973 [21] Appl. No.: 357,987

Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. GoodrowAttorney, Agent, or Firm lohn E. Crowe;i.larnes J. Ralabate; James P.OSullivan [5 7 ABSTRACT A process for obtaining a substantially linearhomopolymer and/or copolymeric material from a cyclic trimer such as1,3,5-trimethyl-1,3,5-tri(N-ethyl-3- carbazyl)cyclotrisiloxane alone orin combination with cyclic trimers or tetramers exemplified by theformulae and in the presence of tetramethylammonium'silanolate orcorresponding alkali metal salt as initiators; the polymeric product,and photoconductive members utilizing such product demonstrate excellentstructural and electronic properties for xerographic purposes.

I 12:.Claims, No Drawings 1 ACTIVE MATRIX AND INTRINSICPI-IOTOCONDUCTIVE POLYMER OF A LINEAR POLYSILOXANE BACKGROUND OF THEINVENTION In the electrophotographic or xerographic art it is customaryto utilize photoreceptor plates having at least an externalphotoconductive insulating layer and a charge conductive supportingsubstrate. Generally, a

photoconductive layer is uniformly electrostatically charged in theabsence of light or other activating radiation end, thereafter, exposedto a light'pattern which can correspond to a negative image. The areasofthe photoconductive layer which are so exposed selectively lose theircharge much more rapidly than non-exposed areas. As a result, thephotoconductive layer at least temporarily retainsa charge correspondingessentially to a latent positive image. This image can then beconveniently developed to form a visible positive image by contactingwith oppositely charged pigmented particles commonly identified as tonerparticles which will adhere mostly to the charged areas. The resultingimage may optionally be permanently affixed to the photoconductor if theimaging layer is not to be reused. This usually occurs with binder-typephotoconductive films where the photoconductive imaging layer is also anintegral part of the finished copy.

Where plain paper copying systems are involved, however, the latentimage is conveniently developed on the imaging surface of a reusablephotoconductor, or transferred to another surface such as a sheet ofpaper.

and thereafter developed. After a latent image is developed on theimaging surface of a reusable-type photoconductor, it is transferred'toanother substrate and then permanently affixed by using any one of avariety of well-known techniques such as by overcoating with atransparent film, or by'therma'l fusion of the toner particles to thesheet. In such a copying system the materials in the photoconductivelayer'must be capable of rapidly changing from an insulative, to achargeconductive, and then back to an insulative condition to permitcyclic use of the imaging surface. Failure to re vert back to theinsulative state before each succeeding I charging sequence will resultin a high dark decay rate commonly referred to as fatigue. In the past,the problem has been controlled, to some extent, simply by selection ofthose photoconductive materials having the best known rapid swtichingcapacity. Typical of such materials are anthracene, poly(N-vinylcarbazole), sulfur, selenium, selenium alloys, metabfreephthalocyanines, etc., and mixtures thereof (U.S. Pat. No. 2,297,691

While organic photoconductive materials such as poly(N-vinylcarbazolegenerally have good dark decay 2 3,408,185; 3,408,186; 3,408,187;3,408,188; 3,408,189; and 3,408,190 are of interest in this area.

For all practical purposesi the amount of sensitization of 1 both vphotoconductive and nonphotoconductive resins depends upon theconcentration of the activator; within limits,the higher the loading,the greater the photoresponse obtained. Unfortunately, however, loadingsexceeding about 10 weight percent of the photoconductive compositionwill usually impair mechanical and/or photoconductive properties of thesensitized composition. Excessive amounts of activator in either aphotoconductive ora nonphotoconductive material of the type disclosed inthe above patents will tend to crystallize outof the photoconduc tivecomposition.- 3

The above inhe rent limitations make it very difficult and often timesimpossible toobtain the much-desired marriage of a high quantumefficiency photoconductor with a tough, transparent, flexible, activematrix material having a low injection threshold. 4

One veryuseful discovery in this area utilizes various protective,polymeric overcoats capable of holding a charge of high field strengthon an external surface and also permitting selective transmittal ofholes from a photoconductive layer through the polymeric-overcoat.

None of the known active matrix materials, however,

are capable of satisfying all of the important physical and electronicproperties needed for modern xerographic or electrophotographic usage. I

OBJECTS OF THE INVENTION It is an object of the present invention toobtain a new class of polymeric materials having the necessary physicaland electrical properties to permit a wider and more flexible use ofxerographic principles for copying pur poses.

It is a further object to synthesize and utilize a new class ofintrinsic organic photoconductors which can be combined with asubstantial amount of an activator without unduly affecting itsmechanical or photoconductive properties. i

A further object of the present invention is to discover and synthesizea new active polymeric matrix material which is compatible with highquantum efficiency photoconductor material and which retains itsflexability and durability.

SUMMARY OF THE INVENTION These and other' objectsare realized by thediscov- .ery, preparation and utilizationofa new class ofsilicon-containing polymeric materials, photoreceptor componentsutilizing such materials as active rnatrices and/or intrinsic photoconductors. When used as described, the materials provide a method forobtaining increased durability, and efficiency in xerographic pho-'which are conveniently represented by the general formulae or wherein R,is defined as a lower alkyl group, preferably an alkyl of 1-8 carbonatoms such as methyl, propyl, isopropyl and octyl; a lower alkoxy suchas a methoxy or propoxy; and as a lower alkyl III IV wherein R isdefined as a lower alkyl group of 28 carbon atoms such as ethyl, propyl,isopropyl or octyl. and defined as an aryl group such as a phenyl groupor a naphthyl group; I

R, and R are individually defined as a hydrogen, lower alkyl of 1-8carbon atoms, halo such as chloro and bromo and cyano groups, suchgroups being preferably attached to one or more of the 3, 6 or 8positions on heteroeyelic ring system (111 and on one or more of thefused aromatic rings of ring system (IV);

R of formulae 1 and 11 is defined as a polymeric end group including theresidue of an initiating chain such as a tetra-methyl ammoniumsilanolate, or otherwise defined as a hydroxyl or ester group such as analkyl carbonyl or an aryl carbonyl group in which the alkyl moietyusefully contains l-l8 carbon atoms and the aryl moiety is a phenylgroup such as phenyl, hydroxy phenyl, an alkyl phenyl or a halo phenylgroup;

R, and R are individually defined as a lower alkyl group, includingalkyl groups of 1-8 carbon atoms such as methyl propyl, isopropyl andn-octyl, and preferably as an alkyl of l3 carbon atoms;

R is a polymeric end group, including hydrogen or an acyl group such asan alkyl carbonyl having an alkyl moiety of 1-18 carbon atoms and anaryl carbonyl such a phenyl carbonyl exemplified by phenylcarbonyl,alkyl substituted phenylcarbonyl or halophenylcarbonyl; and

m, n and 0 are positive numbers commensurate with a number averagemolecular weight of at least about 1,000 and conveniently varying fromabout 1,000 1,000,000 or higher, the numbers 3n and 30 being defined soas to fall within a ratio of about 3:1 to 1:8 in a random or blockcopolymer. For purposes of the present invention the copolymers tend toexceed the homopolymers in molecular weight, a preferred althoughnon-exclusive range being about 1,000 50,000 for the homopolymer andabout 1,000 500,000 for the copolymer, depending upon the ratio ofmonomeric units and the definitions of R and R The above-definedhomopolymers and copolymers are found to be multifunctional in nature(i.e.. as an intrinsic photoconductor or as an active matrix) and areessentially linear, although desired amounts of cross 1 SiO l Si-O l qCH3 Table I Approximate Number Average MW R R R R Ratio P-l 1300 CH OH H2 5 P-5 50,000 lzl Si-O (lntennediateA) Cyclimtion L:

where R is a carbazyl group, steps (c) and (d) prefera- 5 bly proceed asfollows:

In the above partial reaction. Intermediate A preferably includes thefollowing cyclic trimers:

and

Substantially thesame reaction mechanism is also found useful inobtaining cyclized tetramcr or trimer reactants such as (Intermediate B)1 wherein the R and R radicals are defined as in formulae llV supra.

Intermediate A (supra) can be easily converted to the desired'homopolymer or to a corresponding cotetramer, (i.e., Intermediate 8),with an initiating amount of tetra alkyl ammonium silanolate orcorresponding alkali metal salt thereof such as a potassium salt (30-500ppm); optionally the reaction can proceed in the presence of a strongbase such as KOH. For this purpose, the reaction temperature can varyfrom about C to about 160C, depending upon the optimal use of reactionsolvent and the choice of reactants.

When no reaction solvent is utilized, the reaction can best proceed inthe presence of tetra alkylammonium silanolate at a temperature of about80 160C. Preferably this reaction is effected under vacuum for a periodof about 3-5 hours. Extended reaction periods particularly at the highertemperature range, however, favors an increased randomness of unitsattributed to indiscriminate cleavage of long chains by initiatorgroups.

When polymerization is carried out in the presence of a reaction solventsuch as tetrahydrofuran, toluene or dichloroethane, however, it is foundmost convenient to use one of the above initiators, particularly thecorresponding potassium salt of a silanolate initiator at a temperatureoptimally varying from about 20C wholly or partly in place ofIntermediate B.

The following examples further illustrate certain preferred embodimentsof this invention.

in which R is a l-pyrenyl group, is prepared by contacting thecorresponding l-bromopyrenyl reactant with a phenyllithium reactant ingeneral accordance with the mechanism as described following Table l.The

20 resulting cyclic trimer intermediate is then dissolved intetrahydrofurane and then contacted with about 150 ppm potassiumtetramethyl silanolate at room temperature. The reaction mixture isheated to about 60C for 2 hours and then slowly raised to about 120C foran additional hour; the resulting linear homopolymer is isolated bymethanol precipitation and then washed and identified as po1y(methyl-l-pyrenyl siloxane). The product is soluble in CHC1 CHC1 CHClcyclohexanone and tetrahydrofuran, and is conveniently cast fromTHF-tetrachloroethane solution to obtain a clear,

hard, tough, semiflexible film. The product is tested, and. thefollowing parameters noted:

130C, depending upon the solvent. It is also sometimes ,Hmmm Cmma foundadvantageous to slowly raise the reaction temperature to a maximum ofabout 160C during at least the last hour. Preparation of the copolymer.for in g fi lg g stance, is conveniently exemplified by the followingJrwmn Corona I Field v/LI 76 6O equation.

a l i l 3 Si 4 Si() R. CH, CH,

T 1) SiR;, R;,Si() 'N(CH;,), R,Si Si-R R -,Si 20 mo R: O R, ()Si P a sR0 wherein R are defined as above and the ratio of P1 is about 3:1 to1:8. While a substantial variation in the monomeric ratio is possible,it is found that polymers of a higher desirable molecular weight are'obtained when both the trimer and tetramer monomers are utilized andreacted in molar amounts at least sufficient to obtain a copolymerhaving the indicated monomeric ratios. K

For purposes of the present invention, it is also found convenient touse the cyclic trimer,

This data suggests that a substantial number of holes are injected froma selenium photoconductor layer into the polymer overcoat anddischarging the negative charge on the polymer surface.

9 sulting pyrenyl group-containing siloxane homopolymer is coded as p-2.The vacuum stripped, tested and washed product is evaluated in Tablesll-lll below.

EXAMPLE Ill (p-3) 0.01 Mole of cyclic trimer of the formula EXAMPLE IV(p-4) 0.01 Mole of cyclized dimethyl siloxane tetramer of the formulaSi0 L 4 and 0.04 mole of the trimer of Example 1 are dissolved intetrahydrofurane and agitated with about 150 ppm of potassiumtetramethyl silanolate at 60C for 3 hours. The temperature of thethickened reaction mixture is then raised to about 130C for threeadditional hours. The resulting polymeric product (P-4) is washed andidentified as an essentially random linear copolymer which isconveniently represented by the formula li-O l R: f a I wherein theratio of p-to-q is about 3 to l and R is lpyrenyl. The product is testedand results reported in Tables n-m below.

EXAMPLE V (P-S) 0.05 Mole of cyclized dimethyl siloxane tetramer of theformula 10 and 0.07 mole of the cyclietrimer of Example III aredissolved in tetrahydrofuran and reacted as in Example IV. The resultingpolymeric product is washed and identified as an essentially linearcopolymer which is conveniently represented by the formula wherein p andq are in aratio of about l-tol and R. is defined as N-ethyl-3-carbazylgroup. .The product is evaluated and reported in Tables llll[.

EXAMPLE Vl (P-6) 0.003 Mole of the cyclic tetramer and 0.00] mole of thecyclic trimer of Example V are admixed with ppm of tetramethylammoniumsilanolate and heated at about C for 2 hours in a sealed glass ampuleunder vacuum. The resulting copolymer coded as P-b is washed withmethanol and identified as linear poly( methyl-N-ethyl-3-carbazyl-siloxy)dimethylsiloxane co polymer represented by the formula wherein R isidentified as the N-ethyl-3-carbazyl group, and p and q are in a ratioof about 1:4. The methanol-washed product is tested and evaluated inTables ll-lIl.

EXAMPLE Vll (P-7) 0.01 Mole of the cyclic trimer and 0.05 mole of thecyclic tetramer of Example V are dissolved in tetrahydrofuran andagitated in the presence of about 150 ppm potassium dimethyl silanolateinitiator at about 120C. After 3 hours the reaction temperature isgradually raised to about 160C for 1 hour to obtain an essentiallylinear copolymer conveniently represented by the formula wherein R isN-ethyl-3-carbazyl group, and p and q are in a ratio of about l:6. Themethanol-washed product is repeated in Table I.

EXAMPLE VIII (P-S) Example VII is repeated with the addition of 0.001mole of a second cyclic trimer of the formula SiO to obtain a copolymeridentified as P-8. The product is methanol-washed and reported in TableI.

EXAMPLE IX (P-9) Example VII is repeated except that the trimcr reactantis a cyclic compound of the formula EXAMPLE X Six test photoreceptorstrips identified as T l and as control are prepared in the usual mannerby vapor condensation of selenium alloy (60 u) onto an aluminium foilsubstrate. A polymeric overcoat is then cast onto the resulting seleniumphotoconductive layer from tetrachloroethane-tetrahydrofurane solutionsof products P 26 respectively. to obtain polymeric overcoats having anaverage thickness of about 12 u. The resulting test components are thencorona charged. checked for charge retention and discharged by exposurefor seconds with a 200 watt tungsten-iodine lamp at a distance ofcentimeters. The control test is prepared by applying onto the seleniumalloy a homopolymer resin overcoat having a molecular weight of about500,000 consisting of monomeric units of the formula The results arereported in Table III below.

TABLE III Test Polymer The resulting copolymeric product ismethanol-washed and reported in Table I.

Table II Hardness Code Polymer F lexihility Clarity vgv Vg. 0' ex. C vg.C vg. *H homopolymer C copolymer P- P-2 P-3 P-4 P-5 P-6 g good vg verygood ex excellent )Coronai Dark Decay (-l Res.Volt. II) Sec) Light Res.Volt. lU Sec) Light mmocox;

Except for the control, holes injected from the selenium layer into thepolymeric overcoat of T 1-5 are sufficient to discharge a functionallyuseful amount of the surface charge.

EXAMPLE XI Table IV Sample Polymer Charge Discharge Rate Adhesion vu sec84 Spalling P-2 P-2 P-6 P-6 C- l C- l T-(l T-7 T-8 T-9 Control Passedwherein R is defined as a lower alkyl group;

R is defined as an aromatic polycyclic group with fused aromatic ringshaving at least three fused ring nuclei or a heteroaromatic group;

R is defined as a hydroxyl. or other polymeric end group;

R and R,-, are individually defined as a lower alkyl I group; R isdefined as a polymeric end group; and m. n and are positive numberscommensurate with a molecular weight of at least 1,000. the respectivenumerical products represented by 3n and 40 having a ratio of about 3:1to 1:8. 2. A photoconductive member utilizing the polymeric material ofthe formula wherein m is a positive number commensurate with a numberaverage molecular weight of at least about 1.000;

R; and R are polymeric end groups; and

R is an alkyl group of 2-8 carbon atoms or an aryl group.

4. A xerographic photoreceptor component comprising a substrate and atleast one photoconductive layer with an applied active matrix overcoatlayer consisting essentially of a polysiloxane of the formulae m orwherein R, is defined as a lower alkyl. a lower alkoxy.

or lower alkyl carbonyloxy group;

R is defined as an aromatic polycyclic group with fused aromatic ringshaving at least three ring nuclei or a heteroaromatic group;

R is defined as a hydroxyl. or other polymeric end group;

R, and R are individually defined as a lower alkyl group;

R is defined as a polymeric end group; m. n and 0 are positive numberscommensurate with a molecular weight of at least 1,000 the respectivenumerical product represented by 311 and 40 having a ratio of about 3:1to 1:8.

5. A xerographic photoreceptor component comprising a substrate and atleast one photoconductive layer with an applied overcoat layerconsisting essentially of the linear polysiloxane of claim 4 wherein R Rand R are individually defined as an alkyl group of 1-3 carbon atoms;

R is an aromatic polycyclic group having at least three fused ringnuclei; and

R and R are polymeric end groups.

6. A xerographic photoreceptor component comprising a substrate and atleast one photoconductive layer with an applied overcoat layerconsisting essentially of the linear polysiloxane of claim 4 wherein R,,R and R are individually defined as an alkyl group of 13 carbon atoms;and

R is a heterocyclic group.

7. A xerographic photoreceptor component comprising a substrate and atleast one photoconductive layer with an applied overcoat layerconsisting essentially of a linear polysiloxane of the formula si o R6wherein m is a positive number commensurate with a number averagemolecular weight of at least about 1.000;

R and R are polymeric end groups; and R is an alkyl group of 2-8 carbonatoms or an aryl group. 9. A photoconductive member of claim 1 wherein RR, and R in the polysiloxane polymeric material are individually definedas an alkyl group of l3 carbon atoms; R is an aromatic polycyclic grouphaving at least 3 'fused ring nuclei; and R and R are polymeric endgroups. 10. A photoconductive member of claim 1 wherein R, R and R inthe polysiloxane polymeric material 16 are individually defined as analkyl group of 13 carbon atoms; and;

R is a heterocyclic group.

11.. A photoconductive member of claim 10 wherein R is an aromaticpolycyclic group having four fused ring nuclei.

12. A method for obtaining photoreceptor elements having improvedelectronic and mechanical properties for xerographic, copying purposes,said elements having at least a charge conductive substrate and aphotoconductive layer the improvement comprising applying onto thesubstrate at least one of 1 the photoconductive layer or (2) an overcoatlayer having as a polymeric component a linearpolymer represented by theformulae R, is defined as a lower alkyl group;

R is defined as an aromatic polycyclic group with fused aromatic ringshaving at least three ring nuclei or a heteroaromatic group;

R is defined as hydroxyl, hydroxy. or other polymeric end group;

R and R are individually defined as a lower alkyl group;

R is defined as a hydrogen or other polymeric end group and m. n and oare positive numbers comensurate with commensurate molecular weight ofat least 1,000, the respective numerical products represented by 3n and40 having a ratio of about 3:l to 1:8.

Page 1 of 2 UNITED STATES PATENT AND TRADEMARK ()FFICE CERTIFICATE OFCORRECTION PATENT N0. 3,899,328

DATED August 12, 1975 lN\/ ENTOR(S) William W. Limburg It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Abstract, insert subnumbers 3 and 4 on the two formulae to read (31-1and (2H respectively.

Si- O Si-- O I 3 l 4 Column 1, line 48, delete "swtiching" and insert-switching a Column 3, first line below the formulae, delete or".

Column 7, line 12, delete "alkylammonium" and insert alkyl ammonium.

: Column 7, line 59, delete "P:q" and insert -p:q.

Column 7, third formula, delete "0 and insert of) Column 8, line 10,delete "Example I (p-l)" and insert -Example I (Pl)-.

Column 8, line 63, delete "Example II (p-2)" and insert --Example II(P2).

Column 8, last line, delete "ampule" and insert --ampoule--. Column 9,line 2, delete "p-Z" and insert -P2.

Column 9, line 4 delete "Example III (p-3)" and insert Example III(P-3)-.

'[SEAL] Page 2 of 2 UNITED STATES PATENT AND TRADEMARK OFFICECERTIFICATE OF CORRECTION PATENT NO. 3, 899, 328

DATED August 12, 1975 INVENTORG) William w. Limburg It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 9, line 25, delete "Example IV (p-4) and insert -Exa.mple IV (P4)Column 10, line ,24, delete "ampule" and insert aInpoule- Column 16,line 38 after as, insert -a-.

Column 16, line 38, delete "hydroxy" Column 16, line 44, replacecommensurate" with -a.

Attest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner ufParentsand Trademarks

1. A PHOTOCONDUCTIVE MEMBER COMPRISING A SUBSTRATE AND AT LEAST ONEORGANIC PHOTOCONDUCTIVE LAYER COMPRISING AN INTRINSIC POLYMERICPHOTOCONDUCTIVE MATERIAL OF THE FORMULAE
 2. A photoconductive memberutilizing the polymeric material of the formula
 3. A photoconductivemember utilizing the polymeric material of the formula
 4. A xerographicphotoreceptor component comprising a substrate and at least onephotoconductive layer with an applied active matrix overcoat layerconsisting essentially of a polysiloxane of the formulae
 5. Axerographic photoreceptor component comprising a substrate and at leastone photoconductive layer with an applied overcoat layer consistingessentially of the linear polysiloxane of claim 4 wherein R1, R4 and R5are individually defined as an alkyl group of 1-3 carbon atoms; R2 is anaromatic polycyclic group having at least three fused ring nuclei; andR3 and R6 are polymeric end groups.
 6. A xerographic photoreceptorcomponent comprising a substrate and at least one photoconductive layerwith an applied overcoat layer consisting essentially of the linearpolysiloxane of claim 4 wherein R1, R4 and R5 are individually definedas an alkyl group of 1-3 carbon atoms; and R2 is a heterocyclic group.7. A xerographic photoreceptor component comprising a substrate and atleast one photoconductive layer with an applied overcoat layerconsisting essentially of a linear polysiloxane of the formula
 8. Axerographic photoreceptor component comprising a substrate and at leastone photoconductive layer with an applied overcoat layer consistingessentially of a linear polysiloxane of the formula
 9. A photoconductivemember of claim 1 wherein R1, R4 and R5 in the polysiloxane polymericmaterial are individually defined as an alkyl group of 1-3 carbon atoms;R2 is an aromatic polycyclic group having at least 3 fused ring nuclei;and R3 and R6 are polymeric end groups.
 10. A photoconductive member ofclaim 1 wherein R1, R4 and R5 in the polysiloxane polymeric material areindividually defined as an alkyl group of 1-3 carbon atoms; and R2 is aheterocyclic group.
 11. A photoconductive member of claim 10 wherein R2is an aromatic polycyclic group having four fused ring nuclei.
 12. Amethod for obtaining photoreceptor elements having improved electronicand mechanical properties for xerographic copying purposes, saidelements having at least a charge conductive substrate and aphotoconductive layer, the improvement comprising applying onto thesubstrate at least one of (1) the photoconductive layer, or (2) anovercoat layer having as a polymeric component a linear polymerrepresented by the formulae